1. Field of the Invention
This invention relates to a fishing rod having a rod tube formed from synthetic resin-impregnated high strength fiber and to a production method thereof.
2. Description of the Prior Art
Conventional fishing rods called glass rods or carbon rods have been manufactured by producing woven sheets of high strength fiber such as glass fiber or carbon fiber, impregnating those sheets with thermosetting resin to produce prepreg sheets, wrapping the prepreg sheets around a rod tube forming mandrel to a desired thickness, and subjecting the wrapped sheets to several additional processes: a taping process, a baking process, a drawing process, and a surface finish process.
Those rods, which are lighter and stronger and offer a higher resiliency than cane rods, are now employed by many fishermen. Recently, however, still lighter and stronger rods are available on the market.
Some prior fishing rods well known to those skilled in the art have been disclosed in Japanese Patent Laid-open No. 143582/78 and Japanese Utility Model Laid-open No. 54355/86 publications.
The fishing rod disclosed in the former publication is formed from prepreg sheets produced a described above and the prepreg sheet is curved into a tube. The impregnating resin used to produce the prepreg sheets contains microballoons, for example, silica balloons (or microglobules) of 50 to 100 .mu.m in an amount of 20 to 30 wt %.
That rod tube contains less impregnating resin by 20 to 30 wt % because microballoons of a low specific gravity are dispersed in the resin. This results in a lighter rod tube.
Another fishing rod disclosed in the latter publication has a rod tube formed from thermosetting synthetic resin-impregnated high strength fiber. The rod tube is filled with foamed synthetic resin to increase both deflection and compressive strengths thereof.
To impregnate the woven sheets made from the high strength fiber with the thermosetting resin to produce the former prior rod, the sheets were passed through a resin layer containing microballoons into prepreg sheets. Thus the microballoons could not be uniformly dispersed in the impregnating resin layer with some part of the microballoons locally built up. That local buildup degraded the binding effect which the resin had on the microballoons, so that the produced rod was weakened and made easy to break. In addition to those influences, the rod condition (flexibility) was adversely affected.
The latter prior rod was filled with the foamed resin (resin having air or other gas dispersed there through) and the foam density was not uniform through the resin. Thus a desired strength could not be obtained from the produced rods and the products widely varied in strength. In addition, the rod tube had a taper form with the diameter gradually decreased from the butt to the tip. In a rod with a small diameter, uniform dispersion and expansion ratio control of the foaming agent were next to impossible. Some part of the rod tube could not be filled with the foamed resin and the adhesion between the rod's inner wall and the resin was so poor that the resin exfoliated from the rod in service to reduce the rod strength.